In the purification of liquid fuels for engines it is herein proposed to utilize a liquid cyclone and water coalescer in series flow relation between the fuel tank and engine. The cyclone is a device (usually of conical configuration) that imparts centrifugal forces to a fast-moving liquid, thereby causing heavier particles (such as dirt and/or water droplets) to remain near the outer boundary surface of the swirling liquid stream; heavy impurity settles out of the stream. The water coalescer is a device containing a porous media of hydrophobic character, i.e. a preferential ability to be wetted by oil or other non-aqueous liquid; water droplets are repelled by the media so that succeeding droplets impact thereon, eventually producing larger droplets that settle out of the flowing stream.
In the system proposed by applicant the liquid cyclone is used to remove primarily solid contaminant (e.g. dirt or wax particles); the water coalescer is used to remove water droplets that have passed through the cyclone. The cyclone and water coalescer performance is improved by continuously siphoning off some liquid fuel with the impurity; this fuel-impurity mixture is conventionally termed "underflow." The system proposed by applicant includes a relatively small auxiliary separator mechanism for treating the underflow so that fuel in the underflow is returned to the fuel tank; contaminant is discharged from the system substantially free of fuel.
Objects of the invention are to provide a fuel purification system that operates with a high efficiency, that functions with minimum energy expenditure, that takes fairly small total space in or on the engine, that produces minimum pollution of the environment, that can be manufactured at relatively low cost, that contains a minimum number of moving parts, and that has a long service life without maintenance or repair operations.